The invention relates to electric motors and the manufacture thereof, and is specifically directed to an inventive motor casing and the method of its manufacture.
In the manufacture of precision electric motors, it is conventional to employ a pair of motor end casings between which a stator is clamped. A shaft to which a motor is mounted is rotatably carried by the end casings.
In this type of assembly, it is important that the stator be rigidly and stably clamped between the end casings. To that end, the side wall of the end casing has a plurality of circumferentially spaced support points which project laterally inward and lie in the same plane. These support points define a support ledge or shoulder that receives the peripheral edge of one face of the stator. The peripheral edge of the opposite face fits against the ledge of the opposed casing, with the stator thus clamped between the ledges of the opposed casings.
While such an end casing and its method of manufacture have been commercially suitable, the use of circumferential support points has created some degree of difficulty in assembling the motor because the stator must be accurately placed before the components can be clamped together, and this sometimes proves difficult based on tilting or rocking of the stator.
Further, the method of manufacturing this conventional end casing has involved three separate steps, which result in a relatively complicated process. First, a metal blank is placed between complementing dies and is drawn to form a circular end plate and peripheral side wall that extends substantially perpendicular from the end plate. Second, the end plate is pierced in a second operation to form the axial opening for the motor shaft, a circumferential pattern of cooling openings, bolt holes and other openings as may be appropriate to the particular motor. Third, the end casing is held in a stationary position and a plurality of forming points are laterally forced into the side wall by mechanized cams to form the circumferential support points. This involves the use of an additional die set as well as the additional cam mechanism to form the support points.
The invention is the result of an endeavor to produce an improved end casing as well as to simplify its method of manufacture. The improved end casing also comprises a circular end plate and perpendicular peripheral side wall, but rather than a plurality of circumferentially spaced individual support points, a plurality of rectangular, internally projecting lands are formed. Each of the lands defines a ledge or shoulder of significant length as compared to a single support point, and these shoulders are collectively disposed in the same plane to define a circumferential ledge that receives and supports the peripheral facing edge of the stator.
This circumferential ledge reduces of rocking and tilting of the stator relative to the end casing during component assembly and bolting, as well as improved stability of the motor after assembly. The rectangular shoulder lands also increase the overall strength of the end casing, and dimensional accuracy of the assembled motor is maintained not only during assembly but in shipping, handling and operation as well. Another significant improvement resulting from formation of these rectangular lands is the ability to use a smaller metal blank in forming the end casings. Further, due to increased strength and rigidity of the improved casing, a thinner metal blank can be used as compared with the prior art casing. For a significant number of motors that are manufactured, this reduction of size and thickness results in a considerable saving of material and manufacturing cost.
The method of manufacturing the improved casing also represents a significant improvement with respect to the manufacturing method used for the prior art end casing. In particular, the provision of larger rectangular lands actually created a problem since forming lands of this size by a lateral camming operation can distort and bend the casing. However, it was found that the enlarged rectangular lands could themselves be formed in a drawing operation, and that this drawing operation could be combined with the drawing operation in which the peripheral side wall is formed. This combination of operations into a single drawing step completely eliminates the lateral camming operation. This is beneficial not only from the standpoint of eliminating a manufacturing step, but also the elimination of bowing and distortion of the casing end plate during the lateral camming operation of the prior art method. By eliminating the camming operation, and combining the land formation and the drawing operation, the critical dimension of the land is much more consistent and thus better adapted to receive the stator peripheral facing edge without rocking or tilting.
Elimination of the lateral camming operation has also improved the dimensional concentricity of the end casing and reduced end play variation of the output motor shaft. As such, this method increases the quality of the product.
The foregoing improvements and advantages are in addition to those normally expected from the elimination of a manufacturing step, namely, the reduction of labor and associated savings and manufacturing costs. Overall, the improved end casing and method of its manufacture result in an end casing having less material cost and less manufacturing cost, but which is of better dimensional accuracy and of increased quality.